1. Field of the Invention
The present invention relates to shock resistant, flat plate, high temperature, solid oxide electrolyte, electrochemical cells and the flexible interconnection and design of such cells.
2. Description of the Prior Art
High temperature, solid oxide electrolyte fuel cells, and fuel cell generators, are well known in the art, and are taught by Isenberg, in U.S. Pat.Nos. 4,395,468 and 4,490,444. These fuel cell configurations comprise a plurality of individual, series and parallel electronically connected, axially elongated, generally tubular, separately supported, annular cells. Each cell was electronically connected in series to an adjacent cell in a column, through a narrow cell connection extending the full axial length of each cell. These connections contact the air electrode of one cell and the fuel electrode of an adjacent cell, through a conductive ceramic interconnection and a fiber metal felt strip.
A single felt strip, made, for example, of nickel fibers, bonded at contact points, extended axially between the cells. In the preferred embodiment air was flowed inside the cells and gaseous fuel outside. The nickel felt used in the preferred embodiment was about 80% to 97% porous and was generally made according to the teachings of Brown et al., in U.S. Pat. No. 3,895,960, and Pollack, in U.S. Pat. Nos. 3,702,019 and 3,835,514, all involving the use of nickel fibers and metallurgical, diffusion bonding at fiber contact points, at about 900.degree.C to 1200.degree.C.
Self-supporting, low circumferential voltage gradient, solid oxide electrolyte fuel cells were developed by Reichner in U.S. Ser. No. 034,245, filed on Apr. 6, 1987, and assigned to the assignee of this invention (W.E. 53,568). There, an electronically conducting central portion of the axial air electrode was utilized to strengthen the air electrode, eliminating a need for a separate support and to allow ease of electron travel to a ceramic electronically conductive, axial interconnect. The interconnection covered only a small middle section of the air electrode cross section outer top surface, and supported a fiber metal felt, which continued to be disposed parallel to the fuel cell length and gas flow. Elongated configurations, providing a flattened fuel cell with a plurality of interior gas feed chambers was also taught. Here again, all support, electrolyte, and electrode components extended the entire axial length of the cell.
Ackerman et al., in U.S. Pat. No. 4,476,198 and Zwick et al., in U.S. Pat. No. 4,499,663, taught a monolithic array of solid oxide electrolyte fuel cell elements. Here, triangular air and fuel conduits with surrounding electrodes and solid electrolyte were all fused together into an inflexible, ceramic matrix. A plurality of plates were stacked, with ceramic interconnects between them and the whole fused to a single rigid structure. This fused, triangular-element structure was advantageous in that it was very compact, providing a high surface area to volume, contained no inactive materials, and did not require a separate support structure, but, it was fragile, and provided little tolerance to thermal gradients or component shrinkage during fabrication and operation. Also, a local defect caused during manufacturing or due to degradation in operation could necessitate replacement of an entire monolithic structure.
The generator configuration of Ackerman et al., similarly to Isenberg in U.S. Pat. No. 4,395,468, had a generating section, containing the fuel cells, disposed between an oxidant preheating section and a fuel inlet section. A triangular configuration of materials in an electrochemical cell structure was also taught by Ehrenfeld in U.S. Pat. No. 3,206,334, where a nickel and iron oxide catalyst coated, cellular structure supported an electrode and electrolyte, and was a conduit for oxidant and fuel.
None of these configurations provide a flat plate, repairable design that combines higher power density in larger individual cells, along with a flexible cell array structure that would not be sensitive to thermal gradients and stresses during start-up and operation.